Matt Riddle withdrew from his scheduled Bellator MMA debut after suffering a rib injury on Monday.

Riddle, who was slated to fight Luis Melo Jr. in the quarterfinals of the Bellator's season-nine welterweight tournament, subsequently announced his retirement from mixed martial arts.

"I'm retiring from MMA today," Riddle wrote on Facebook. "Cracked my rib and can't fight Sept. 20. Bellator said they can't find me a fight till the next tournament and I can't afford not fighting that long and need a job. Sorry if I let anyone down but it isn't paying the bills."

Riddle hangs up his gloves having fought professionally only under the UFC banner. The 27-year-old debuted on The Ultimate Fighter 7, where he memorably knocked out Dan Simmler just nine seconds into the second round of his elimination fight.

Riddle subsequently lost to Tim Credeur in the season's opening round, but went on to compile a career 7-3 record with two no contests, both of which were initial victories overturned due to positive tests for marijuana. Riddle earned his UFC release following a second failed drug test, then signed with Texas based promotion Legacy FC before having his contract bought out by Bellator MMA.